1. Field of the Disclosure
This document relates to an optical film and a backlight unit having the same.
2. Description of the Background Art
A liquid crystal display (LCD) is an electronic device that changes various electrical information generated from various elements to visual information by using a change in a liquid crystal transmission and transfers it.
The general LCD comprises a liquid crystal panel that displays an image according to a drive signal and a data signal applied from an external source and a backlight unit disposed on a rear surface of the liquid crystal panel in order to illuminate the liquid crystal panel.
The backlight unit comprises a light source unit, a reflection sheet, and an optical film.
The light source generates light of a certain wavelength.
The reflection sheet reflects light that has not been made incident on the optical film, among light generated from the light source, to allow the light to proceed in the direction of the liquid crystal panel.
The optical film comprises a diffusion sheet, a prism sheet, and a protection sheet.
Light outputted toward the liquid crystal panel after being generated from the light source passes through the diffusion sheet. At this time, the diffusion sheet distributes the incident light, preventing the light from concentrating partially and making luminance uniform.
As the light passes through the diffusion sheet, its luminance is sharply degraded, so in order to prevent the degradation of the luminance, the prism sheet is used.
FIG. 1 is a perspective view of the prism sheet according to the related art, and FIG. 2 is a sectional view showing a display state of the liquid crystal panel when the prism sheet in FIG. 1 is used.
With reference to FIG. 1, the prism sheet 10 comprises a prism support unit 20 and a plurality of prism configuration parts 30 formed side by side on the entire surface of the prism support unit 20.
The prism configuration parts 30 comprise side parts each with a first side 32 and a second side 34 and substantially having an equilateral triangular shape when viewed from the front side. The angle between the first and second sides 32 and 34 is generally 90°, and may vary according to a selection.
As the plurality of prism configuration parts 30 are continuously formed on the prism support unit 20, there are formed valleys 38 and peaks 36 alternately. Light made incident on the prism support unit 20 of the thusly constructed prism sheet 10, it is refracted while passing through the prism configuration parts 30. Accordingly, the light made incident at the low angle is concentrated toward the front side, enhancing luminance within the range of an effective viewing angle.
However, when the prism configuration parts 30 of the related art prism sheet 10 contact with a smooth surface of a different optical film, traces remain on one surface of the optical film according to the configuration of the peaks 36 of the prism configuration parts 30, causing a wet-out phenomenon that the optical film is damaged, which results in appearance of bright lines 40a that a corresponding portion is seen brighter than a peripheral portion when viewed from an outer side of the liquid crystal panel 40.
In addition, when the wet-out phenomenon occurs as the prism configuration parts 30 contact with the different optical film, the configuration of the peaks 36 may be deformed because the peaks 36 come in contact with the optical film.
Moreover, the screen display capability deteriorates because a moiré phenomenon occurs due to interference of periodical patterns between pixels constituting the liquid crystal panel 40 and the prism configuration parts 30 of the prism sheet 10 and also because of a Newton's ring phenomenon.